501 



dp _2, d£l 1 



X J\ 0,30967.256 ;. 



2R dp dii p, , /1\ 



As for — = ü we have — = — - or — = / -— , it follows, 

 I p £i p, y T, 



4 2R 



that k, = — for — = 0. 

 ' 3 ;i 



2/e 



In the case, that — becomes large, we obtain 



dp k, 8 r dT 



^ = -i.— . ('30967 



p k, :t R' T 



or introducing 



::t 1 if T 



8 0,30967''p'p„273 

 where (>„ is the density of the gas at 0° and 1 djne per cm.' 

 we get the formula 



^ ^ 0,30967.273' o„ R"" k.\ c ' 



V + T 



calculating, like Knudsen, with Sutherland's formula (which however 



is no longer applicable at temperatures below those of liquid air) 



and calling the viscosity at 0° C. ïj„. 



Knudsen has determined tlie value of /i\ and /Ij for hydrogen and 



k, 

 oxygen and found — — 2.3 and k, = I. 



It is easily shown, that our formula (1) differs from Knudsen's 



formula only by the factor , which has no iniluence for 



^ 2R 



2R 

 high values of — . 

 * X 



It is therefore obvious, that the factor l\ in (1), if this equation 



2R 

 is to hold for all values of — , cannot be a constant, seeing that 



27? 

 for ail gases it approaches the value i for -^ =r and that for 



2R 

 high values of — it becomes 2.3 for o.xygen and hydrogen. 



It is further to be remembered that in the theoretical deduction 



